This section introduces aspects that may facilitate a better understanding of the disclosure(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
With development of wireless communication, billions of devices will be served via wireless connections for various services. Most of them are located at indoor scenario. For instance, it is very common to have several wireless devices at home and more than half of a hundred in an office floor or a conference room (e.g. cellular phone, tablet computer, smart television and etc.). In future, there will also be much more numbers of indoor devices who have needs to be served by a wireless connection to achieve the vision of connected world. Currently, wireless fidelity (WiFi) technology is the dominant wireless indoor access technology. As well-known, the WiFi performance will be degraded severely with an increasing number of active users due to frequent collisions resulted from contention-based Media Access Control (MAC). The spectrum efficiency of WiFi technology is usually less than Long Term Evolution (LTE) technology.
For the time being, companies have been proposing to run LTE over unlicensed bands by aggregating licensed and unlicensed band. As is known, 2.4 GHz and 5 GHz are the main unlicensed bands for WiFi systems currently. Since 2.4 GHz is already very crowded, 5 GHz may be a promising focus for LTE systems. Band at 5 GHz is usually divided into a multitude of channels. Countries apply their own regulations on allowable channels, allowed users and maximum power levels within these frequency ranges. The detailed channelization for different countries can be found in the following address: http://en.wikipedia.org/wiki/List_of_WLAN_channels.
From the list of Wireless Local Area Network (WLAN) channels, the channel bandwidth for WiFi channel is either 10 MHz or 20 MHz, which is coincidently aligned with that for LTE systems. More important, there are multiple orthogonal channels available in each country. For one particular WiFi access point (AP), it normally uses one or several of them (channel bundling) and does not use all of them. Thus status (e.g. load situation, interference) of different channels change in different time and place can be different.
All WiFi network equipments, including terminal devices and APs (e.g. routers), communicate over specific channels. Similar to that of a traditional television, each WiFi channel is designated by a number that represents a specific radio communication frequency bandwidth.
There are two different methods for channel selection in WiFi, i.e. automatically and manually. Both of them are always available for user configuration on WiFi routers. Operating system and utility software on WiFi routers keep track of WiFi channel settings being used at any given time. Under normal conditions, users don't need to worry about these settings. However, users and administrators may wish to change their Wi-Fi channel numbers in certain situations. Channel use is up to user behaviour and the status is not easy to predict. In other words, the channel may be free at one time and busy in another time.
There are large unlicensed bandwidths in 2.4 GHz and 5 GHz. Operators and vendors show strong interest in running LTE over these bands. However, mechanisms to run LTE over unlicensed band are not determined yet.
U.S. Pat. No. 8,374,212B2 discloses a frequency hopping method for radio resource control (RRC) signalling which is used to configure a user device for N secondary cells SCells on license-exempt channels in a frequency hopping channel. Then cross-carrier scheduling is sent on a primary cell PCell to schedule a frequency hopping resource block on the i-th license-exempt channel.
The current proposals for LTE over unlicensed bands mainly focus to aggregate licensed carriers and unlicensed carriers, and unlicensed carriers can be probably only used as secondary carriers. For example, frequency hopping signaling is proposed in U.S. Pat. No. 8,374,212B2 for configuring a user device for secondary cells on unlicensed bands. The following problems exist for such carrier aggregation based solution:
First, LTE cannot run over unlicensed carrier without licensed carrier support, and carrier aggregation is a mandatory feature for both evolved Node B (eNB) and user equipment (UE). This means complexity in both UE and eNB sides.
Second, if such an eNB is used for local access (e.g., at home, company), LTE users cannot access public data network (PDN) over unlicensed carriers via the eNB without paying to mobile operator due to mandatory licensed carrier. This means that such eNB is mainly developed to increase operator revenue rather than to serve as an access node for private local access. From this perspective, it is probably still less competitive than WiFi AP for private local access in home, office, shop, theatre, stadium, restaurant, hotel etc.